Regarding photosemiconductor element sealing resin compositions, compositions each including a bisphenol A type epoxy resin having excellent adhesiveness or mechanical strength, an epoxy resin which has no UV absorption, for example, a hydrogenated bisphenol A type epoxy resin or an alicyclic epoxy resin, a curing agent, and a curing catalyst, have been frequently used. However, along with the increase in the luminance and output power of LED elements, these compositions have problems such as discoloration and cracking, due to the light, heat and the like emitted by LED elements.
As a solution for solving these problems, there is known a resin obtainable by introducing an epoxy group into a silicone resin which yields a cured product that does not absorb UV radiation and has flexibility. For example, a silicone resin having one or more units of a cyclic ether-containing group such as a glycidyl group or an epoxycyclohexyl group (Patent Literature 1); a reaction product of an epoxyalkoxysilane and silanol (Patent Literature 2); and a combination of an alicyclic epoxy-modified silicone resin and an alicyclic epoxy resin (Patent Literature 3) are known. However, since silicone resins have very high gas permeability compared to epoxy resins, as the silicone content increases, it becomes more difficult to use silicone resins in applications where low gas permeability is needed. Thus, an addition reaction type phenyl-based silicone resin composition has been disclosed as a resin composition having low gas permeability (Patent Literature 4); however, even this silicone resin composition is still not satisfactory in the aspects of low gas permeability and adhesiveness.